Sculpting cartoon mouth
You're on the right track with sculpting. However your first priority should be to create a simple base mesh of the entire character before moving on to details like the mouth and its stitches. You can do this by blocking everything out with primitives and then joining them later.
Here's an example of stylized base meshes (Credit to VeryHotShark on Gumroad):

A great habit to get into is to focus on the largest details first so you can get your proportions correct and ensure you have the best topology possible to start out with before detailing and sculpting.

Hey guys Im trying to make a Jack Skellington blend and I have no idea how to sculpt his mouth, nothing feels right should I just draw his seams on the texture or actually sculpt them

To directly answer your question about the mouth, it all comes down to how detailed you want your mesh to be. How close you will be featuring his face on camera? Are you animating his face? Does he talk?
It might be easiest to just draw the seams on the texture, but you will have less detail than if you had sculpted it. If you sculpt the seams, it will look quite a bit more realistic and hold up better in close up camera shots.